Printing telegraph exchange system



Jan. 24, 1933. G. s. VERNAM PRINTING TELEGRAPH EXCHANGE SYSTEM Filed May12,l 1930 6 Sheets-Sheet 1 ATTORN EY BY e'.

Jan. 24, 1933.

G. S. VERNAM Filed May l2, 19550 D CONCENTRATION 6 Sheets-Sheet 2 `FswITcHING TRUNK 0* 23e l 20e, 21o 207 QI um S2326 1 -@,243 zowanv 2552467 225 247 l 215 Q32 @7J 2'3 21a 249 T-@.167 les 7I2 7&1242

E G CONCENTRATION BOARD CENTRAL STATION OPERATORS PRINTER sI-:T PRINTERsET 1577 CALL (RELEASE IIIZ J C J -\'l/ CUSTOMERS STATION Io. M Q I- I4I 5a |04- II77 IIe I P I T 133 o l l 5 |29l L '5B mles "9) I i Q 59 C.rv 2r f BIF T27 a *q |34 |39 :t I 2 I IAO h`, Ie I35 *|25 INVENTOR 136|24 HOV. ACW-DC' GILBERT $.VERNAM I` Y .,I37 BY I -ATTQRN E Jan. 24,1933. G. s. VERNAM 1,895,112

PRINTING TELEGRAPH EXCHANGE SYSTEM Filed May l2, 193C 6 Sheets-Sheetv I5STATION TO TOLL- UNE CORD a i966 306 mvENToR 32" smsen-r SNERNAM HSTATION To STATION CORD B Flc. 3 ATTORNEY Jan. 24, 1933. G. s. VERNAM f1,895,112

PRINTING TELEGRAPH EXCHANGE SYSTEM Filed May 12, 195s e sheets-sheet 4 fJ 73o 7oz Eef \474 I. K 503 ToLL LINE To ToLL LINE coRD L v TOLL BOARDOPERATORS PRINTER SET INVENTOR GILBERT S. VERNAM B FIG. 4

vATT'oRNET G. s. VERNAM 1,895,112

PRINTING TELEGRAPH EXCHANGE SYSTEM Jan. 24, 1933.

Filed May l2, 193C 6 Sheets-Sheet 5 Tou. LINE clac-unI TO M L TOLL BOARDOPERATORS PRINTER SET (9 GILBERT s. VERNAM FIG. 5

Patented Jan. 24, 1933.'

, UNITED STATES PATENT y oEElcE GILBERT S. VERNAM, OF RIVER EDGE, NEWJERSEY, ASSIGNOR TO INTERNATIONAL COMMUNICATIONS LABOBATOBIES,. INC.,

NEW YORK Application led Hay 12,

This invention relates to printing telegraph exchange systems and moreparticularly applies to manually operated printing vtelegraph exchangesystems.

, a toll switch board in the central oice one customers printer may beconnected directly to another customers printer in the same city or in adifferent city. The service provided by this toll switch board willcorrespond in general, to a toll telephone exchange service.

A feature of this invention is the reduction of line current to afraction of its usual amperage when the line is idle.

A second feature of this invention is the operation of the toll linecircuits full duplex for the purpose of controlling the lamp signals sothat the calling and supervisory signals may operate independently inthe two directions over the line, with the automatic conversion of thecircuit to half duplex operation, when printing connections are made.

A further feature of this inventionis a cord circuit for establishingvfull duplex through connections between two telegraph toll lines at anintermediate switching center with provision for the connection of anoperators printer intq this cord circuit so that the operator at theintermediate station can communicate with both terminal stations.

A further feature of this invention is the use of monitoring keys in thecord circuits whereby the toll board operator can readlly cut herprinter in or out of any of the cord circuits. A feature closelyassociated with this one is the use of a splitting key in the toll boardoperators printer circuit permitting the toll board operator tocomprinter with either cord of a A further feature of this invention isthe OF NEW YORK, N. Y., A CORPORATION 0F PRDITING TELE-GRAPH EXCHANGESYSTEM 1930. Serial No. 451,693.

arrangement whereby the customers may advise the concentration boardoperator by lamp signals as to the nature of the service desired.

A further feature of this invention is an alternative arrangementwhereby the customer may, by selective means predetermine where at thecentral station his call is to be answered.

A further feat-ure of this invention is the association of the signallamps with the cord circuits rather than with the line circuits, and thearrangement whereby the lamps are lighted only when action is requiredon the part of the operator.

An additional feature of this invention is the provision of a motorcontrol whereby the printer motors at the customers stations are startedwhen the station line is connected to a printer or to a toll board cordat the central oiiice and the provision for stopping the motor from thecentral oiice or at the customers station.

Outline of system l Referring to the drawings, Figure 1 shows inschematic form two groups of customers i' `of the form of the inventionas illustrated i Figs. 2 to 5.

Fig. 2 shows in detail the circuit of a customers station, and thecircuits of various parts of a central station viz. a concentrationboard, a concentration board operators printer set, a switching trunkand a central station printer set.

Fig. 3 shows in detail the left hand portion of station to toll linecord circuit yI and the circuit of station to station cord H.

Fig. 4 shows in detail the right hand portion of the station to tollline cord circuit I, the toll line to toll line cord circuit K and theleft hand portion of the toll board operators printer set circuit L.

Fig. 5 shows in detail in circuit J the apparatus at one end of a tollline, similar apparatus being located at the distant endof the line atstation M the direction of which is indicated but which is not shown;this gure also shows the right hand portion of toll board operatorsprinter set circuit L.

Fig. 6 shows in detail the circuit of customers station() similar tocircuit C of Fig. 2, and in circuit P a portion of a toll board and twoconcentration board si al panels at a central station showing their usewith a selective call system.

Fig. 1 illustrates in outline, the proposed manual printer exchangesystem. kWhile for purposes of illustration only `live customersstatlons are here shown as associated with central station A there maybe a lar e number of such stations and all the circuits have been soarranged that the whole system can be expanded with facility to handlean indefinite number of new customers stations as well as new centralstations. Thus the concentration board station connections may bereadily increased and the number of concentration board and centralstations operators printers can be increased to serve the additionallocal stations. Also the number of station to station, station to tollline and toll line to toll line cords, may vary in number according tothe requirements of the traffi, only one of each type being shown,however, in this fi re. Obviously there may also be any num r of stationto station toll lines coming into each toll board. It will therefore beunderstood that in the description of the system in the ensuing pagestypical hook-ups will be presented and no attempt will be made to pointout all the connections that might possibly be made.

In regard to the expansion of the system illustrated attention isparticularly called to certain specific points 1n the circuits where eansion may take place. At the following points the ground connections mabe made through auxiliary signal circuits; ig. 2, circuit D, at 724;circuit F, at 710, 711 and y712; Fig". 3, circuit I, at 713; circuit H,at 714; Fig. 4 circuit I, at 715; circuit-K, at 716 and 717 Fig. 5,circuit J at 718; circuit L at 719; Fig. 6, circuit P at 720, 721, 722and 723. At oint'204 in circuit F, Fig. 2, point 708, in clrcuit J, Fig.5 and point 709 in circuit P, Fig. 6, additional lamps and jacks may beinserted. In' Fig. 3, circuit H, at points 703 and 704 additionalmonitoring keys might be inserted for use with additional cord cir`cuits, likewise in Fig. 4, at points 705, 706 'sind 707. No attempt hasvbeen made, however, to point out all the specific points at wlhichexpansion of the system might take p ace.

Likewise it will be understood that there may be any number ofadditional central stafi tions with associated local lines, and thatthese various central stations may be con.- nected one to another overthe various toll lines insome cases directly and in other cases throughan intermediary central station or several intermediary centralstations, and

any one customers station associated with one of the central stationsmay therebybe connected with any other customer station associated withthat particular central station or with any other central station.

In Fig. 1 customers stations 1 to 5, are shown connected by telegraphlines 6 to 10 to the concentration board jacks 11 to 15. Connected to anadditional jack 16 on the concentration board is a concentration boardoperators printer 17 by means of which the concentration board operatormay communicate with the toll board operator. Cords 18,

19 and 20 at the concentration board lead to tration board with the tollboard for various types of service. They may connect any two ofcustomers stations, 1 to 5 through the toll board by means of station tostation cord 35.

They may also be used for connecting one of the customers stations 1 to5, to a central station other than central station A through station totoll line cord 38, connection with the distant central station beingmade through one of the telegraph toll lines 39,- 40 or 41 associatedwith the toll board jacks 42, 43 and 44, respectively, each of whichlines may be connected to a different central station. The third cord 45at the toll board is known as the toll line to toll line cord and may beconnected to any two of the toll lines 39 to 41 through plugs 46 and 47.In-the toll board cord circuits 35, 38 and 45, monitoring keys 48, 49and 50 are respectively inserted. By means of these monitoring keys thetoll board operators printer 51 may be connected to any one of the threecord circuits. Central station B together with its customers stationsand lines and toll lines, is a duplicate of vcentral station A and itsauxiliary rlines and has therefore not been specificall described.

The operation of the system for the pur-v pose of sending telegrams orcablegrams through central station A will be clear if i-t is stated thatany oneof the customers stations, 1 to 5, desiring to send a. telegramor cablegram is connected by the concentration board operator with oneof the central sta- Lagan ing trunkl such as 27, a station to toll lineVcord 38 and toll line 39, 40 or 41 to the toll board of central stationB- and thus in reverse order from the toll board at central station B,over a switching trunk to the concentration board of central station Band so to the customers station associated with central station B withwhich communication is desired.

Where central station A is used las an intermediate station forconnecting two other central stations, connections will be made over twoof the toll lines 39, 40 and 41 by -means of a toll station to tollstation cord 45 the circuit thus passing through only the toll boardofthe intermediate station.

Umtomers station circuit In Fig. 2, customers station C is shownconnected to a concentration board D and associated therewith is shownconcentration board printer set E, switching trunk F and central stationprinter set G.

At the customers station C, polar rela 101 is connected in series withcustomers telegraph line 102 joining the 'customers station C withconcentration board D at the central station. This relay 101 has twowindings, connected in series, one of low resistance 103 and one of highresistance 104, and is equipped with a biasing spring 105 which tends tomove the relay armature 106 against contact 107. Relay 101l will bereleased and will close contact 107 on the application of a positivepotential to line 102 at the central station. In the normal or idlecondition of the customers station circuit, l

through the winding of marginal relay 113y and conductor 114 to normallyclosed jack contact 115 and thence through resistance 116 and overcustomers line 102 through windings 103 and 104 of relay 10,1 in series,over conductor 117 through printer-line magnet 118, transmitter 119 andtrecall or break key 120 to ground 121. Under these conditions, relay101 will be operated but marginal relay 113 will not be affected by thisstrength of current.

In the case of a call, either from a central station circuit of thisfigure (21, 22 or 23 of Fig. 1) or from the toll board (see Fig.'1), acord plug will be inserted in one of the line jacks 123 of theconcentration board with the result that a positive potential will beapplied to customers station line 102. The method of applying thispositive potential tothe cord circuits will be described later.

The application of the positive potential reverses the direction of thecurrent in relay 101, which was previously held operated by a negativepotential, and it thereupon releases armature 106 which closes contact107. A current is thereby passed from terminal 124, of a local A. C. orD. C. source Lover conductor 125 through resistance 126, conductor 127,through winding Vof control relay 128, conductor 129, to'back contact130 of relay 131, across armature 132, conductor 133 to contact 107 andthus through conductor 134, resistance 135 and conductor 136 to theopposite terminal 137 f of the current supply. The

closing of this circuit operates control relay 128 which closes itscontacts 139 and 138 there- .by respectively, putting into operationprinter motor 140, and short-circuiting high resistance Winding-104 ofrelay 101. vThe line current now increases to its usual working `valueof about 60 milliamperes. Resistance 116 in customers line 102 isincluded in the circuit to regulate the current to this value and tocompensate for variations in the resistances of the line wires todifferent' stations. Under these conditions, printer signals may be sentfrom the sending contacts of customers station'transmitter 1'19 or fromthose of a central oiiice or distant printer, and these signals willoperate the respective printers without operating relay 101 since spring10@ gives the relay a positive bias. If a negative potential is'againapplied to the line, however, the reversal of current will operate relay101 to pull up armature 106 and break the circuit through the controlrelay -128 at contact 107, causing the control relay 128,to release,thus stopping printer motor 140 and reinserting' the high resistancewinding 104 of relay 101 into the line circuit. The circuit is nowrestored to its original or idle condition and a negative current ofapproximately 6 milliamneres is passing through the circuit.

.In the case of a call originating at customers station C, the customersoperator'operates calling key 141 in a direction to close contacts 142,which short-circuits the high resistance winding 104, of relay 101, thusincreasing the line current from approximately 6 to 60 milliamperes. Thecalling key 141 (prrinter 122 in central station printer that the leverwill lock in the calling'position or in the normal position but whenoperated to the releasing side (for purposes to be described later) thekey is non-locking and will restore itself to the normal'position whenreleased by the operator.

If the key is left in the calling position, the increased line currentwill operate marginal relay 113 at concentration board D, which relay,will in turn operate relay 143 of the concentration board circuit whichlocks itself through a circuit traced from ground 144 through contact145, jack contact 146, conductor 147, current source 109 and ground 108.Under these conditions current will be applied to toll lamp 148 atconcentration board D over a circuit which may be traced from ground149, contact 150 of relay 143, conductor A151, front contact 152 ofrelay 113, conductor 153, conductor 154, current supply 109 and ground108, lighting the lamp and indicating that a connection with the tollboard is d esired.

If, on the other hand, calling key 141 at customers station C isoperated to the calling position and then restored to normal, the relays113 and 143 will operateas described and then relay 113 will release,with the result that the message lamp 155 will be lighted, indicatingrthat the customer wishes a connection with a central station printer torecord an outgoing telegram or cablegram. In either case, relay 101 ofcustomers station C will not be released until a positive current isconnected through the concentration board to customers line 102, aspreviously described. The insertion of a cord plug into the jack 123 atconcentration board D will obviously release relays 113 and 143l by`breaking the operating circuits of these relays at contacts 115 and 146respectively extinguishing whichever lamp is lighted.

After a connection has been established and relay 101 has been releasedandc'ontrol relay 128 operated at the customers station the customer maysend a disconnect signal to the. central station by operating key 141momentarily to the release position thus closing contact 156 whichcloses a circuit commencing at terminal 137 of the local current sourceand consisting of conductor 136, resistance 135, conductor 134, contact107, conductor 133, conductor 157, contact 156,

conductor 158, Winding of relay 131, resistance 126, and conductor 125to the opposite pole 124 of the current source. Relay 131 is thusoperated and locks itself through its front contact 159 thus breakingthe operating circuit of control relay 128 at contact 130 and releasingsaid control relay which in turn -stops printer motor 140 by breakingcontact 139 and connects the high resistance Winding 104 of relay 101into the "line circuit by breaking contact 138. The resultant reductionin the current in customers line 102 acts to light supervisory signalsin the various cord circuits at the toll board as will be describedlater. When the circuit is .disconnected at the central otlice, anegative current from source 109 is again applied to customers line 102,relay 101 will be operated and the locking circuit of relay 131 brokenat contact 107 of relay 101, thus releasing relay 131 and restoring thecircuit to normal.

Central station prt-'Itter set crm't As was indicated in Fig. 1 thecentral station apparatus and circuits `consist generally ofconcentration board D, concentration board operators printer set E,switching trunk F, central station printer circuits G, station tostation cord circuits H, station to toll line circuits I, toll linecircuit J, toll line to toll line `cord circuit K and toll boardoperators printer set circuit L. Circuit G of Fig. 2 illustrates thecircuit of the printer set at the central telegraph office used forsending and receiving telegrams and cablegrams. In the idle condition,all of the relays in this circuit are released asV illustrated .and theprinter motor 160 is stopped. To prepare this circuit for thetransmission of messages the plug 161 which is located at the centralstation concentration board, is in serted into jack 123, by theconcentration board operator thus connecting the central station printerset circuit G with customers station C through line 102, the controlrelay 162 willbe operated to start motor 160, light the guard lamp 163,and to supply current for the local circuits of the printer as well asto connect a positive current from current source 164 to the customersstation line 102. The circuit for operating the control relay may betraced from ground 108 .at concentration board D through current' source109, protective resistance 165, conductor 147, jack contact 166, sleeveof jack 123, sleeve contact of plug 161, conductor 169, junction point199, conductor 170, key 171,

conductor 172, back contact 173 of sleeve relay 174, conductor 175,conductor 176, and

so through winding of relay 162 to ground 177.

' It will be seen that the operation of relay 162 closes Contact 168which connects current lsource 164 through contact 168 to junction 178from which current flows through resistance 179 to guard lamp 163 andthus to 102 to customers station C as above indi' cated Where motor 140is started. v The stations now are ready for the transmission of when itis inserted in the jack is so low that it is impossible for the operatorto receive a shock from the circuit, except possibly from an inductivedischarge from the winding of control relay 162 or the kwinding ofsleeve relay 174 when the cord plug 161 is pulled down. This could beavoided, if necessary, lb connecting a resistance from the sleeve of pug 161 to the ground. The same general method of preventing shocks isused for all the jacks and plugs on the toll board.

en communication between the stations has been completed, the centralstation printer operator momentarily operates release key 171. Thisbreaks a connection through conductor 172, contact 173, and armature175, which short-circuits the winding of sleeve relay 174, thuspermitting relay 17 4 to operate in series with the control relay 162and on being energized, sleeve relay 174 itself opens the short-circuitat back contact 173, so that it will not release when the contacts ofrelease key 171 are again closed. It also shortcircuits the winding ofcontrol relay 162 b grounding itself through its front contact 18 andground 188, thus releasing control relay 162, which opens contact 168thus cutting olf the current from guard lamp 163 and conductor 181 andstopping the printer motor 160. Sleeve relay 174 also applies a negativecurrent from source 189 through the winding of the marginal recall relay190 to the station line circuit by means of. conductors 191, frontcontact 192 of sleeve relay 174 and conductor 185, and vtip of plug 161.This current o erates relay 101 at the customers station to pull uparmature 106 which opens a circuit to sto printer motor 140 aspreviously described. Sleeve relay 17 4 also passes a negative currentfrom current source 189 through resistance 193, conductor 194, contact195, conductor 196, and disconnect lamp 197 Ato ground 198, whichcircuit lights disconnect lamp 197 located at the concentration board asa signal to the concentration board operator to pull down cord plug'161.As a negative potential has already been applied to customers line 102from source 189 with the result that the line current has been reducedto approximately 6 milliamperes by the release of the control relay 128at customers station C, the marginal relay 113 at concentration board Dwill not operate when plug 161 is withdrawn at, the concentration board.When this plug is withdrawn, however, negative current from source 109is cut oli from the sleeve ofv plug 161, sleeve relay 174 is releasedand by reason of the breaking of the circuit at its contacts 195 and192, respectively,'negativecurrent from current source 189 is removedfrom disconnect lamp 197 and from tip of 1p1ug'161, and the circuit isrestored to its normal or idle condition.

If the concentration b oard opaerator should be slow to disconnect andthe customers operator should wish to place another call, call key 141at customers station C may be operated to close contacts 142 to increasethe negative 6 milliamperes currentto a negative current ofapproximately milliamperes as previously. described. Under theseconditions, the recall relay 190 of printer set G, which is a marginalrelay operable on a current of 60 milliamperes but not on a current of 6,milliamperes, and which is connected through front Contact 192 ofsleeve relay 174 to the customers line, will operate and short-circuitsleeve relay 174 through a circuit traced from junction 199,`throughconductor 170release key 171, conductor 172, contact 200, armature 201,conductor 202, Winding of control relay 162 and -ound 177. Sleeve relay174 having been re eased will disconnect the circuit operatingrecalnlwrelay 190 through contact 192. Recall relay 190 is shunted byresistance 203 to make it slightly slow to release thereby preventing itfrom releasing until sleeve relay 17 4 has b een completely released.'The release of sleeverelay 174 also removes the short-circuit fromcontrol relay 162 which thereupon operates,

. closes contact 168 which passes a current from currentsource 164 tojunction 178 thus lightthrough conductor 181, to start printer motor 160and also passing a positive current through transmitter 122, conductor183, contact 184, conductor 185 to the tip of plug 161 and so throughcustomers line 102 to customers station C where, by previously de- Theswitching trunk circuit is shown at F of Fig. 2, (see also switchingtrunks 27, 28 and 29 in Fig. 1). This circuit serves to extend ltheconnections inl either direction ybetween the concentration board andthe toll board. If the toll board has more than one ying theguard lamp163 and passing a current position, the circuits can be multipled at thetoll board as indicated in the drawings, (204 .of circuit fF, Fig. 2).If there are several concentration boards, each board will have its` owngroup of trunk lines to the toll board,

handle the peak load.

sufficient trunk linesv being provided If the toll, llamp 148 atconcentration l board D, which is associated with customers station line102 vlights'indi'catingl that l(511stomers station C wishes to place atoll call,

loffrom customers line 102 through jack 123,

tip of plug 205, conductor 208, contact 209 of jack 210 throughconductor 211, similarly through contacts of jacks at any other tollboard positions as indicated by dotted lines v"l at 204 and nallythrough contact 213 of jack 212, conductor 214 and winding of marginalrelay 215, resistance 216, negative current source 217 to ground 218.Marginal relay 215 is thereby operated, closing contact 219 and thusclosing circuit from ground 220, through positive current source 221,resist- Aance 222, contact 223, conductor 224, contact 219, conductor225, call lamps 167 and 226 to I ounds 186 and 227 respectively, therebyare located at the toll board. Relay 206 in operating alsoshort-circuits resistance 228, thus preparing a circuit for lateroperating the guard lamp 229 located at the concentration board. I

This call 'may `be answered ylay inserting `pug 230 (Fig. 3) of stationto station cord or plug 231 (Fig. 3) of station to toll line cord I intothe switching trunk jack 210 at the toll board or into the correspondingjack for this trunk at any other toll board posi? tion such as jack 212.The detailsof these -cord circuits will be explained later. The i,insertion of oneof these plugs places ground 40 on kthe sleeve of jack210 through sleeve of plug 231, conductor 233, winding of relay 451,conductor 452, winding of relay 234 and 'ground 235. From the sleevey ofjack 210 the ground isl connected through contact lli 236, conductor237, contact 238, conductor 239, winding of relay 240, resistance 241,to positive current source 221 and so to ground 220, thus o eratin busyrelay 240 of switching trunk F, whicIx, by opening contact 223,.extinguishes call'lamps 167 and 226 and also closes a circuit throughbusy lamps 242 and 243, traced from ground 220, through positive currentsource 221, resistance 244, contact 245 of relay 240, conductor 246, tojunction point 56 247 and thus over conductor 249 and through busy lamp242 to ground v248vand from junction point 247 again over conductor 249through busylam 243 to ground 250 and slmilarly through usy lamps atother 'posiv60, tions as indicated by the multi le connections 'at 204.The insertion of `a cor plug i-nto jack 210 or the corresponding "jacksulch as 212 at another position also opens contacts`209 thus removingground from marginal relay 215 fwhich consequently releases. The tips ofghting the call lamps 167 and 226 which cord plu 230 and 231 (Fig. 3)are both connecte to positive current sources as will be later detailed.On the insertion of one of these plugs in jack 210, the source ofpositive potential is applied to the customers line 102 throughconductor 208, contact `207, tip of plug 205 and jack 123. As previouslyexplained, this posltive current will start printer motor 140 atcustomers station C.

In the case of a call from the toll board for a station line, the tollboard operator inserts a cord plug 230 or 231'(Fig.'3) into an idleswitching trunkl jack such as 210. This closes contact 236 and thusplaces the ground associated with the sleeve 'of plugs 230 or 231 onconductor 237y and passes it through'resista-nce 228 (relay 206 beingunoperated) over conductor 239 and through the windings of busy relay240, through resistance. 241, source of potential 221 to ground 220.Resistance-228 in this case, so

limits the current from source 221 'that' marginal sleeve relay 234(Fig. 3) of cord I ormarginal rela 251 (Fig. 3) of cord H, cannotoperate. usy relay 240 ron ybeing operated, closes its vcontact 245 and,as previously explained, lights the busy lamps 2/12 similarly throughguar lamps at other positions as indicated b the dotted line at 710 toound 255, thus ighting the guard lamp at t e concentration boardadvising the'concentration board operator of the out oing call. The tollboard operator then in orms the concentration board operator of thenumber of the called station. This maybe done by using` a separate orderwire operating-by telephone, by printing telegraph, by manual telegraphmeans or the switching trunk cord plug 205 may be inserted into jack 256ofthe concentration boardprinter set E (see also 17 o'f Fig. 1), theoperation of which vwill be obvious to those skilled in the art, andthe,

necessary information sent directly over the trunk circuit.

The concentration board operator will then insert the switchin trunkplug 205 into jack 123 of the callecustomers station line, this willapply a negative current from current source 109 at concentration boardD to the sleeve of jack 123 which in turn will pass the current throu hthe sleeve of plug 205 to the winding o sleeve relay 206 of switchingtrunk F, thus operating relay 206 which opens contact 254 and thusextinguishes guard lamp 229. Relay 206, by closing contact- 238 shuntsresistance 228, placing suicient additional current from source 221, onthe coils of marginal relay 234 (Fig. 3) of cord I or 251 (Fig. 3)of'cord H, to operate it, thus applying a positive current from source437 (Fig. 4) or sourceV 'tomers station C where it will start the y intothe line again at jack 210.

motor 140 as previously described.

When the call is completed, the toll board operator pulls down the cordplug fromswitching trunk jack 210 which breaks contact 236, releasingbusy relay 240 and closingcontact209 of Jack210 thus re-establishing thecircuit through the winding of marginal relay 215 to the negativecurrent source 217. This operates relay 101 and releases relay 128 atthe customers station, and as the call.

key 141 is in its normal position, the current 4will be reduced to about6 milliamperes;

Relay 215 may operate momentarily immediately after the removal of theplug, but it will release when the line current is reduced. As relay 240is released, and sleeve relay 206. remains operated, the circuit fromcurrent source to guard lamp 229 is closed andthe lamp will light.YContact 245 beingopened on the release of relay 240 the busy lamps 242and 243 will be extinguished. Under these conditions, the concentrationboard operator should pull down the switching trunk cord plug 205,restoring the circuit to normal. However, if the opera-tor at thecustomers station should operate the call key 141 (closing contact 142)to place a new call, before the switching trunk cord plug 205 has beenpulled down, high resistance winding 104 of relay 101 will be removedfrom the cusomers linecircuit and the Acurrent increased fromapproximately l6 milliamperes to vmilliamperes and marginal signal relay215 of switching trunk F will then operate to light call lamps 167 and226 at the toll board and by opening contact 807 will also extinguishthe guard lamp 229, whereupon the toll board operator-will plug Stationto station cord circuit stations and that, further', thne front andbackplugs 268 and 230 respectively, have been inserted .into the jacks 210oftwo separate switching trunks, which are extended through theconcentrationboard D to station C of the called and calling customers,respectively. Relays-'206 and 240 of switching trunk F (Fig. 2) will,therefore, be energized as well as the control relays 128 at thecustomers station C (Fig. 2) and the sleeve relays 251 and 259 of thestation to stationcordcircuit H will also be operated. The polarrepeaing relays 257 and 258 will be energized in a direction to holdtheir respective, armav tures 259 and 260 against marking vcontacts 261and 262 respectively.

The two left hand windings 263 and 264 of relay 257 and windings 265 and266 of relay-258 are differentially connected, windings 263 and 265being connected to ground through the concentration board and thestation line, which circuits may be traced, for winding 263, throughconductor 808 through front contact 267 to the tip of plug 268 and sothrough a switching trunk F (Fig. 2), and concentration board D tocustomers line 102; for winding 265 through conductor 269,

4contact 270 of monitoring key 306, conductor 271,'front Contact 272 ofrelay'251, to tip of plug 230, and so through a second switching trunk F(Fig. 2) vand concentration board D to a second cusomers line 102.Windings 264 and 266 are carried to ground through artificial lines 273and 274 consisting respectively of resistance 275 andV inductanc'e 276and resistance 277 and inductance 278. From junction point 279 where theartificial lines unite a circuit may be traced over conductor 280 tojunction point 282 and through conductor 283 and contact 284 of sleeverelay 259 t0 ground 285. The ,circuits through the windings 263` 264,265and 266 are not exactly balanced, the current through 263 and-265 beingnearly twice that of windings 264 and 266. As long as'both circuits oneach relay remain closed, the relay armatures will remain against theirmarking contacts 261 and 262 respectively, but if the circuits 'oflinewinding 263 or 265 is opened by an. open signal impulse sent from itsrespective cusv tomers station C, the relay armature 259' or 260respectively, will be moved to its spacing contacts 286 or 287respectively under the influence of the current in the artificial linewinding.

' It i's evident, therefore, that each of these relays will respond tosignals sent fromthe station to which its line winding is connected.

When so operated, each relay will repeat these signalsthrough the.windings of the other relay into the other station line, thus, if' theline to which winding 263 of relay 257 is connectedis closed at thecalled customers station C, (Fig. 2) a current will be sent through acircuit as follows: from ground 290, of station to station cord Hthrough source'of positive potential 291, conductor 292, junction point293, resistance 294, armature 260,1narking contact 262,A conductor 296,back contact 297 of cut relay 298, conductor 299 to junction point 288and thus through winding 263 of relayv 257 and through conductor 808,contact 267 of relay 259 to the tip of plug.2 68 and thus through aswitching trunk F (Fig. 2), through the concentration board D tocustomers line 102 and so to ground 121 atcustomers station C. Relay 257(Fig. 3) will then close its marking contact 261 and cause a current topass from source of positive potential 291, associated with ground 290,through conductor 292, junction point 300, resistance 301, conductor302, armature 259, marking contact 261 of relay 257, back contact 303 ofcut relay 298, conductor304 to junction point 289 and thus throughwinding 265 of relay 258, conductor 269, contact 270 of monitoring key306, conductor 271, contact 272 of relay 251, to the tip of plug 230 andthus over a second switching trunk F (Fig. 2), through concentrationboard D to a second customers line 102 to the calling customersstation-C where the printer magnet 118 will be operated and finally toground 121. A

Winding 305 of relay 257 and winding 295 of relay 258 havevlessturnsthan the other two windings of these relays and the currents throughthem have comparatively small magnetic effects in a direction tending toaid the line windings 263 and 265, respectively, in'

holding the respective armatures against the marking contacts. Thisdoesnot interfere with the repeating action described above, but serves tohold the armatures against the marking contacts whenrno current isliowing through either of the other windings. Therefore, when the relay257, for instance, repeats signals through relay 258, the latter relaywill not respond to these signals as its armature 260 is held againstits marking contact 262 by winding 295 when windings 265 and 266 areopen at relay 257, that is to say, when spacing contact 2,86 of relay257 is closed, armature 260 is held against marking contact 262 bywinding 295 and. when armature 259 reverses and contact 261 is closedarmature 260 is still held against contact 262, but this time by winding265. The inductanoes 276 and 278 associated with rela s 257 and 258,which are in series with arti cial line windingsl 264 and 266respectively, prevent the current in these windings from rising morerapidly than'in the line windings 263 and 265 when the line circuits areclosed, thus balancing the inductance of the printer line 1(1114agnet118 at -the customers stations C Itg'should be noted that the linecircuit from the tip of cord plug 230 to the line winding 265 of relay258 extends through normally closed contact 270 of the monitoring leskey 306. When this key 306 is operated, the sending contacts 307 andline relay 318 of the operators printer in operators set circuit L (Fig.4) are connected in series. with the line at this point. This circuitcan be traced as follows: from junction point 308 (Fig.v 3) ofmonitoring key 306 through contact 309, conductor 310, contact 311 ofmonitoring key 312, (also through contacts similar to 311 of monitoringkeys for other cord circuits indicated by dotted lines 704 and 705)conductor 313, contact 314 of split key 315 (Fig. 4), conductor 316,winding 317 of polar relay 318, conductor 319, contact 320 of monitoringkey 321, (also through contacts similar to 320 of monitoring keys forother cord circuits as indicated by dotted line 706) conductor 322,contact 323 of monitoring key 321, conductor 324, key 325, toll i boardoperators transmitter 307, conductor 326, contact 327, conductor 328,`-contact 329 of monitoring key 312, conductor 330, contact 331, toconductor 271 in station to station cord circuit H. The contact springsof the monitoring key 306 are so arranged and adjusted that the key canbe operated or re` stored to cut the toll board operators printer unit(key 325, transmitting contacts 307, line relay 318 and printing magnet578) inor out of the circuit without momentarily interrupting thestation line circuit. Also if two or more monitoring keys are operatedltogether in error, this will not interfere with the communicationvbetween the customers,

but the operators printer will be conne/ctedv to the cord circuit whosemonitoringkey is nearest to the operators set in the circuit, viz., ifthe monitoring keys 306-and 312 are both operated at the same time, theoperators.

the opening of monitoring key 312. It isA to be noted that a monitoringkey associated with a toll line to toll line cord K (Fig. 4) shouldnotbe operated at the same time as that of one of the other types ofcords as thi/s would permit signals to be repeated from one cord circuitto another. l

The split key 315 of the toll board operators printer set circuit L(Fig. 4) may be used if the operator wishes to communicate with onecustomers station C andat the same time cut off the other customersstation C. For example, if this key is operated in a direction to openthe contact 314 and close contacts 332, 333 and 334, the operatorsprinter will be connected through cord plug 230 of station to stationcord H,.sincethe opening of contact 314 and the closing of Contact 332cutsk off 'the return circuit to relay 258 (Fig. 3)

and instead closes the circuitvthrough consplit keyV 315 (Fig. 4)through conductor 340, Awinding 341 (Fig. 5) of supervisory relay 342,conductor 343, to contact point-344 and through resistance 345, whichresistance is. equivalent to that of a station line and' then to ground346.

The circuit just traced energizes relay 342 which opens contact 347 thuspreventing relay 348 from operating. The operator may now communicatedirectly with the station connected through cord plug 230 (Fig. 3) andthese signals will not be repeated through the station connected throughcord plug 268 (Fig. 3). The station connected through the latter plugmay, however, recall the operator by holding recall key 120 at customersstation C (Fig. 2) operated for a few seconds. This will open the lineand release supervis-x ory relay 342 (Fig. closing contact 347. After ashort interval, relay 348 which is a slow to operate relay will operateover a circuit traced from ground 349 (Fig. 4) of the split key circuit,contact 334, conductor 350, contact 347 ig. 5) through winding 351 ofrelay` 348 through resistance 352 and through source of positivepotential 353 to ground 354. The operation of relay 348 closes theoperating circuit of guard lamp 355 at Contact 356 thereby lighting thelamp and relay 348 locks itself at contact 357 to hold the guard lamplighted until split key 315 is restored to normal.

It the split key (Fig. 4) is operated in the opposite direction to closecontacts 358, 359, 360, and open contact 327, the line winding 235 ofrelay 258 (Fig. 3) will be connected through the operators printer andlthrough resistance`345 to ground 346 while the line circuit operatingthrough cord plug 230 (Fig. 3) will be connected to positive currentsource 338 (Fig. 5) through Contact 359 (Fig. 4) conductor 701 andwinding 361 of relay 342 (Fig. 5). Under these conditions, the operatormay communicate through relays 257 and 258 (Fig. 3) with the stationconnected through cord plug 268, while the station connected throughcord plug 230 will be in position to operate guard lamp 355 (Fig. .5) aspreviously described for the 'reverse-situation.

Referring again to station to station cord H, (Fig. 3) the-action ofsleeve relays 251 and 259 will be described. Assuming that a call from acustomers station has been extended through the concentration board D(Fig. 2) and over a switching trunk F to the toll board, the toll boardoperator will then insert cord plug230 (Fig. 3) in jack 210 of theswitching trunk F. This will close the circuit from ground 281 (Fig. 3)through the winding of .sleeve relay 251, sleeve of plug 230 and contact236 (Fig. 2) of jack 210, through winding of relay 240 to current source221 and ground 220 at the switching trunk F. This will operate relay 240of the switching trunk which will extinguish call lamps 167 and 226 andlightthe busy lamps 242 and 243 as previously described. It will alsooperate sleeve relay 251 (Fig. 3) of station to station cord circuit H.This relay current to the line and artificial line windings of the otherrelay.

The circuit of the line winding of relay 258 extends to callingcustomers station C (Fig. 2) as previously traced `where by reason ofthe positive current carried over said line from current source 291(Fig. 3) of station to station cord circuit H, relay 101 (Fig. 2) isreleased and printer motor 14() started as previously described.: Thecircuit of the line winding of relay 257 (Fig. 3) extends through bacllicontact 365 of sleeve relay259 and through resistance 366 which isequivalent to a station line.

The operator may now operate the monitoring key 306 and communicate withthe calling customers station C as previously described. Afterascertaining the number of the called line, cord plug 268 will beinserted into jack 210 (Fig. 2) of an idle switching trunk F. Aspreviously explained in connection with the operation of sleeve vrelay251, this will extend a ground connection to the relay 240 of switchingtrunk F throughA the sleeve of cord plug 268 and contact 236 of jack2,10 but as the circuit has not yet been extended to a called customersstation C, relay `206 of the switching trunk. circuit F has not beenoperated and consequently .c

resistance 228 is still in the circuit and sleeve relay 259 (Fig. 3)will not be operated since insucient current passes through resistance228 to operate it. Guard lamp 229 (Fig. 2) will be lighted by theoperation of relay 240 and consequent closing of contact 252. When theconcentration board operator replies, the toll board operator gives herthe number of the called station. Whereupon the concentration boardoperator inserts switching trunk plug 205 into jack 123 associated withthe called station line 102, which connection extends negative. currentfrom current source 109 at concentration board D through jack v123 andsleeve of plug 205 to relay 206 of switching trunk F which operates toshort-circuit'resistance 228 enabling sufficient current to be passedfrom current source 221 of the switching trunk through contact 236 andjack 210 of switching trunk F and sleeve of cord plug 268 (Fig. 3) tooperate sleeve relay 259 of station to station cord circuit H therebyclosing contact 267 and connecting winding 263 of relay 257 with thecalled customers station. On completion of line connections with thecalled customers station C, positive current is passed from source ofpositive current2-91 through conductor 292 to junction point 293,resistance 294, armature 260, marking contact 262,

lconductor 296, contact point 297, conductor 299, Winding 263 of relay257, conductor 808, contact 267 through the tip of cord plug 268,through switching trunk F (Fig. 2) and so through the concentrationboard and customers line 102 to the called station C where the motor 140is started as was previously described whereupon the calling and calledcustomers stations C may now communicate with each other. The toll boardoperator should restore monitoring key 306 to normal as soon ascommunication is satisfactorily established.

When the call is completed, the operator at each customers stationmomentarily operates relay key 141 closing contact 156 which operates tolock relay 131 and release control relay 128 as previously described.This stops station motor 140 and reduces the line current toapproximately 6 milliam-peres. Assuming that the calling customersstation C connected through cord plug 230 (Fig. 3)

Vof station to station cord circuit H, operates releasekey 141 first,relay 258 (Fi 3) of station to station cord circuit H, wil release butas this opens a circuit at contact 262, to both windings 263 and 264 ofrelay 257, relay 257 cannot release at this time by reason of the eiiectof winding 305 even though the called station, connected through cordplug 268, also operates its release key 141.

Relay 258 thereupon closes a circuit from its spacing contact 287 asfollows: from current source 291 associated with .ground 290 throughconductor 292, junction point 293, resistance 294, armature 260, contact287, conductor 367, resistance 368, winding of relay 363, junction point370, conductor 371, contact 37'2 of monitoring key 306, conductor 373,conductor 374 through contact 375 of relay 251 to ground 281. Relay 363is a slow act-ing relay which will not operate on short impulses due toprinter signals but will operate when armature 260 of relay 258 remainsagainst its spacing contact 287 for a longer interval. Relay 363 beingoperated, closes -its contact 376 and thereby places ground 377 in thecircuit of supervisory lamp 378 associated with cord plug 230 thusapplying current from source 291 to the lamp and lighting it. Relay 363also closes contact 379, which places ground 380 on the ffgcut relay298. The cut relay operates, and

closing contacts 381 and 382, applies positive current directly towindings 263, 264 and 265, 266 of f relays 257 and 253 respectively overcircuits traced as follows: for relay .257 from ground 290 throughvcurrent source 291,

conductor 292, junction point 293, resistance 294, conductor 383,contact pointr382, conductor 299 to junction -point 288 and so throughwindings 263 and 264; for relay 258 from ground 290Y through currentsource 291, conductor 292, ljunction point 300, re-

sistance 301, conductor 302, to contact point 5 381, conductor 304 tocontact pointl 289 and so through windings 265 and 266 of relay 258.Relay 363 in effect, therefore, cuts the repeater so that a signal sentinto one side of the repeater will now have no effect on the linecircuit of the other side of the repeater. If the release key 141 (Fig.2) at the called customers station C, connected to cord plug 268 (Fig.3) of station to station cord H, has been operated by this time, relay257 will now release by reason of the insertion of high resistancewinding '104 (Fig. 2) into the circuit at the called customers station Cand after an intervaly relay 3.62 (Fig. 3) will operate and lightsupervisory lamp 384 associated with cord plug'268, in the same manneras described for the lighting of supervisory lamp 378. lVhen bothsupervisory lamps 37 8 and 384 are lighted, the toll board operator willpull down both cord plugs 230 and 268. This will operate relay 101 (Fig.2) at both customers stations C which action will release relay 131 atboth customer-s stations and will light guard lamps 229 associated withcustomers stations lines at' the switching trunk circuit F, to signalthe concentration board operator to disconnect, aspreviously described.The cord circuit relays 251 and 259 (Fig. 3) will also be restored tonormal which will remove the ground from the relays 362 and 363 causingthem to release and extinguish the supervisory lamps 384 and 37 8.

If, instead of sending a disconnect signal, the operator at eithercustomers station wishes to recallthe toll board operator, the recallkey 120 (Fig. 2) at customer-s station C may be opened for a period oftime suliicient to allow slow operating relay I362 or 363 (Fig. 3)respectively to operate the corresponding supervisory lamp 384 or 37 8,the supervisory lamp, under these conditions, might be flashed byoperating and releasing the' recall key slowly several times insuccession.

Telegraph toll Zine circuit One terminal of a telegraph toll linecircuit is shown at J of Figure 5 (see also J in Fig. 1). As shown onthe drawings, two polar relays are used, so connected as to form adifcapable of transmitting signals in both directions could be used. Forexample, a metallic two wire line equippedl for duplex operation mightbe used, or two wires, each arranged to 'send signals in one direction.A full duplex carrier telegraph channel might be used or even a two-wayradio telegraph channel. It

Ais thought that the method of arranging this .the winding of the polechanger relay 385 is connected through jack contact 386 of jack 387.Pole changer 385 is also connected by a circuit traceable throughcontact 386, conductor 388,' (which also extends through contactssimilar to 386 of any intermediate jacks which may be placed in thecircuit at point indicated by broken line 7 08'-it should also be notedthat additional lamps may also be inserted at this point) contact 389 ofjack 390, conductor 391, resistance 392, winding of busy relay 393 toground 394. Busy relay 393 is a sensitive relay that will operate on asmall current. It, therefore, remains operated to keep the busy lamps395 and 396 extinguished while the line is idle and at the same timeplaces a ,ground on winding 398 of pole changer 385. Under theseconditions, however, the current from the lower or biasing winding 397of pole changer 385 is stronger than that in the upper or line winding398 and therefore the pole changer armature 399 remains against itspositive or spacing contact, 400. Current from the positive currentsource 401 passes through resistance 402 and contact 400 to noise-killer403, and in parallel through windings 404 and 405 of line relay 406 toline 407 and artiicial line 408 respectively. The line relay 406 is notaffected by this current but as the pole changer at an identical stationM (not shown), at the distant end of the line, is also against Vitsspacing contact, the armature of the line relay at station Mcorresponding to relay 406 at station J, viz. 406M will also be againstits open or spacing contact, and the receiving leg, or in other words,thel conductor 409M leading to the tip of jack 387M will be open.

If the cord plug 412 (Fig. 4) is inserted in toll line jack 387, acurrent from source 414 will be carried over conductor 410 to sleeve ofcord plug 412, in other words, the sending leg of the duplex set will beconnected through contact 411 to the sleeve of jack 387, and if thesleeve of plug 412 is connected through a suitable resistance to ground,this ground will be placed o-n winding 398 of pole changer 385 throughcontact 411 of jack 387 and conductor 410. and

the circuit will he completed through resistance 413, current source 414and ground 415.

It is to be'noted'that resistance 698 connected between current source414 and winding 397 of pole changer 385l is of much higher resistancethan resistance 413, and it is to be further noted that ground 478replaces' ground 394 whichis' associated with the'busy relay 393 andthat resistance 699. associated' with ground 478, is a. lower resistancethan resistance 392 associated .with ground 394. Consequently, with theplacing. of ground 478 on winding 398, more current iiows through thiswinding than through winding 397, and armature 399 is therefore operatedagainst its negative or marking contact 416. This will operate the linerelay 406M at the distant end of the line to close the receiving leg409M which will in turn energize Vcall lamp relay 417M to light the calllamps 418M and 419M. The circuit for operating relay 417M maybe tracedas follows: ground 420M, source of potential 421M,fresistance 422M.contact 423M, conl'ductor 409M, contact 424M of jack 387M, conductor425M, contact 426M of jack- 390M, conductor 427M, winding of relay 417Mthrough resistance 428M to ground 429M. It should be noted that theinsertion of the cord plug 412M into iack 387M will release the busyrelay 393M breaking jack contact 386M consequently lighting the busylamps 395M and 396M, over a circuit traced from ground 430M throughcurrent source 431M,

conductor 432M, resistances 433M and 434M.Y busy lamps 395M and 396M,conducto-r 435M, contact 436M to ground 394M. It 'will be noted that theinsertion of plug 412M into jack 387M will also operate pole changer385M at therdistant end of the line to send a marking signal back overline 407 to relay 406 in circuit J. The further operation of the tollline circuit can best be explained in connection with the operation ofthe cord circuits.

Station to toll Zine cord mer is used, it will be necessary for theoperator tochange plugs as soon as she finds out that the customerwishes a long distance connection. In either case. cord plug 231 (Fig.3) of station to toll line cord I will ulti'- mately be inserted intoswitching trunk jack 210 Fig. 2). The insertion of plug 231 into jack210 closes contact 236 and, as previously described, places a positivepotentialV on the sleeve of plug 231 throughv current source v 221 ofswitching trunk circuit F. This current is passed from the sleeve ofcordplug 231vover conductor 233 (Fig. 3) through thevv windings of relay451, through conductor 452 and through the windings of marginal relay234 to gro-und 235 operating relay 234. Relay 451 will also be operatedto close contact 453 which operates a circuit from ground 454 throughpositive potential 455, resistance 456, contact 453, conductor457,'contact 458 and so through supervisory lamp 459 to ground 460. Thusthe supervisory lanip459 will be lighted immediately on connectionsbeing made between cord circuit I and switching trunk F. Relay 234, byclosing contact 443 connects a positivel current from current source 437(Fig. 4) to the customers station line 102 (Fig. 2) through a cil"- cuittraced as follows: ground 438, current source 437, resistance 439,conductor 440, contact 441, conductor 442, contact 443 (Fig. 3)conductor 444, contact 445 of monitoring key 312, conductor 446. contact447, conductor 448. winding of rel'av 449, conductor 450 to cord plug231 and so through switching trunk circuit F (Fig. 2), concentrationboard D to customers line 102. This circuit also operates relay 449(Fig. 3) which closes contact 461. which places ground 462 on relay 463`which in turn opens contact- 458 to extinguish supervisory lamp 459. Theoperator at cord I may, however. communicate with the calling customersstation by operating monitoring keyv312 if necessary.

Cord plug 412 (Fig. 4) is now inserted into the jack 387 (Fig. 5) of anidle toll line to the desired distant city. Repeating rela-y 464 (Fig.4) in cord circuit I operates like relays 257 and 258 of station tostation cord circuit H. which was previously described and therefore itsmethod of operation need not be described here in detail. lVinding 465of relay 46 4 correspondsto windings 263 and 265 of relays 257 and 258respectively, winding 466 of relay 464 corresponds to windings 264 and266 of relays 257 and 258 respectively, and winding 470 of relay 464corresponds to windings 305 and 295 of relays 257 and 258 respectively,and the corresponding windings have approximately the same resistances.It should be noted, however, that as line relay 406 of the toll line isreleased when plug 412 isfirst inserted in jack 387,

the receiving leg 409 (Fig. 5) of the duplex set is open and there willbe no current through the two windings 465 and 466 ot relay 464 (Fig. 4)but the relay will be held operated by a current from source 437 passedover conductor 467, through resistance 468, conductor 469, throughwinding 470 of relay 464 to ground 471. The contact 472 of relay 464being closed, a circuit may be traced from ground 415 (Fig. 5)associated with pole changer 385 through current source 414, resistance413, winding 398 of pole changer 385, conductor 410, contact 411, sleeveof cord plug 412 (Fig..4), conductor 473, contact 472, conductor 474,contact 475', conductor 476, through supervisory lamp 477, tolground478, which will be lighted, indicating to the toll board operatorof cord I that the distant toll operator at station M has not yetanswered. Supervisory lamp 477 is shunted by resistance 699 so that polechanger 385 will receiveits normal working current of about milliampereswithout passing excessive current through lamp 477.

'Since ground is placed on the line Winding 398 (Fig. 5) of pole changer385 it will operate and send a marking impulse'over line 407 to stationM. The marking signal transmitted by pole changer 385 will cause linerelay 406M to close contact 423M, thus operating relay 417 M andlighting the call lamps 418M and 419M. The operator at station M willrespond by plugging cord plug 412M into toll line jack 387M. In thiscase, as line relay 406M is opera-ted closing contact 423M, and sleeverelay 234M (Fig. 3) of the station to toll line cord circuit I is notoperated, the repeating lrelay 464M (Fig. 4) will be held operatedthrough its righthand winding 465M and through the back contact 479M orrelay 234M to ground 480M. Relay 481M also operates over a circuittraced from junc-v tion point 482M through winding 466M of relay 464M,resistance 483M, inductance coil 484M, winding of relay 481M to ground485M. The operation of relay 481M will close contact 486M to placeground on slow release relay 487M over a current operating from ground485M to contact 486M, through conductor 488M, winding ot relay 487M,conductor 489M, resistance 490M, conductor 467 M and through source ofpotential 437 M to ground 438M. Relay 487M willt-hen operate to breakContact 47 5M, removing supervisory lamp 477M from the sleeve circuit ofjack 387M (Fig. 5) and replacing the ground .478M (Fig. 4) associatedwith the supervisory lamp 477M by ground 491M through resistance 492M atcontact 493M. The supervisory lamp 477M is thereby extinguished, andpole changer'385M operates.

The operation of pole changer 385M (Fig. 5) sends a marking signal backover line 407 to operate the line relay 406. This closes the receivingleg 409 connecting positive current fromv current source 421, throughContact 423, over receiving leg 409, through jack 387, to tip of plug412 (Fig. 4) and so to windings 465 and 466 of relay 464. The relays 481and 487 will be operated as previously explained in connection with theoperation of station M, the latter relay extinguishing supervisory lamp477. Relay 487 will also extend the receiving leg circuit 409 fromwinding-465 of relay 464, over conductor 702 through junction point 730,conductor 731, contact point 496, conductor 442 and contact point 443(Fig. 3) and so through monitoring key 312 to the line circuit extendingto the calling customers station C.

With the monitoring .keys 312 operated, the toll operators at bothstations make contact with each other by printer over the toll line 407and their conversation will be recorded by the printer at the callingsubscribers station.- If it is desired to avoid f having thisconversation reported at the calling subscribers station, the outwardoperator may operate split key 315 (Fig. 4) in a di? rection to operatethe right-hand springs, closing contacts 358, 359 and 360 and thusconnecting a positive current through relay 342 (Fig. 5) to the callingcustomers station line 102 and connecting station M through cord plug412 and the operators printer 307 to ground 346 (Fig. 5) as previouslydescribed. s f

After the outward operator has transmitted the number of the calledstation, the o erator at station M will connect plug 231KI Fig. 3) to anidle switching jack 210M Fig. 2) and establish a connection toA thecalled subscribers station C in the same manner as previously describedfor local calls. When the cord plug 231M is inserted into jack 210M,sleeve relay 234M does not operate until switching trunk F at thedistant station is plugged up at the concentration board. at which timeit does operate to extend the toll line circuit through to the calledsubscribers station C starting the station motor in the usual manner, aspreviously described.

The customers stations may now communicate with each other by printer.The outgoing printer signals through each station operating repeatingrelay 464 (Fig.4) of thel cord circuit I, which will in turn open andclose the sending leg circuit at contact 472 to operate pole changer385. Incoming signals from the toll line 407 (Fig. 5) will operate linerelay 406 which will repeat these signals overl the receiving legcircuity 409 directly through the windings 465 and 466 of relay 464(Fig. 4) to the station line 102 (Fig.

2) without operating relay 464, as previously described in connectionwith repeating relays 257 and 258 (Fig. 3). It will be seen,therefore,"that relay 464 is in effect a half set repeater and has theeffect of converting ,y the full duplex circuit into a half duplexcircuit. The operators at the two customers` stations C may bothtransmit and receive but both cannot transmit at the same time. The tollboard Ioperators at the two central stations should cut out of thecircuitD by restoring their monitoring keys 312 as soon as communicationisy satisfactorily established.

The outgoingsignals will operate marginal relay 449 (Fig. 3) as'previously described, and the incoming signals from the distant stationvwill operate relay 481 (Fig. 4) as well as relay 449. Relays 449 and481 will send impulses through the windings of relay 487 ever, and willnot release on printer signals. If the operator at either of thecustomer s stations should wish to recall his toll board operator, he`may do so by slowly opening and closing the contacts of the recall Vkey120 (Fig. 2) at customers station C.- This will release marginal relay449 (Fig. 3) for a suflicient yinterval to allow relay 463 to releaseand light the supervisory lamp 459, as previously described. vIt will.also release relays 481M (Fig. 4) and 449M at the distant end of theline. This will permit relay 487M to release, closing contact 475M andthus ligblting supervisory lamp 477M. Re-

also connects positive current from source 437M to rela 449M (Fig. 3)throu h resistance 439M (Fig. 4), conductor 440 contact 441M, conductor442M, contact 443M (Fig. 3) conductor 444M, contact 445M, conductor446M, contact 447M, and conductor 448M, thus operatin relay 449M. Relay463M should prefera ly be adjusted to be' Such a local signal may beanswered by the o`erator by means of monitoring key 312 ig. 3) and iftrouble is being experienced,

` split key 315 (Fig. 4) may .be o erated, if

necessary, to determine whethert e trouble is in the local stationcircuit' or on the toll line circuit. i

At the conclusion of the call both stations should clear the circuit byrestoring their call keys 141 (Fig. 2) to normal and momentarilyoperating the release portions of keys 141', thus releasing contacts 142and closing contacts 156. This will lock up relay 131 and release thecontrol relay 128 at each customers station to stop motors 140 andreduce the line current, as previously described, by

los

no l

inserting high resistancewindings 104 of rel lays lOl-into the circuits.The reduction in the line current will release marginal relay 4 l449(Fig. 3) of station to station toll line cord circuit I. The stationwhich rst disconnects will also release relay 464 (Fig. 4) which will inturn open contact 472 and thus open the sending leg circuit and causepole changer 385 (Fig. 5) to release and armature 399 to close itscircuit at contact 400, thus sending a spacing signal over toll line 407to the other station. This will release relay 406 at the .distant end ofthe line with the result that the receiving leg circuit will be openedat contact\423, and thus stopping the flow of current from source 421,through windings 465 (Fig. 4) and 466' of relay 464. Consequently relay464 will be held operated by winding 470, as previously described.Relays 481 and.487 will release, however, to light supervisory lamp 477,as previously described. The supervisory lamp 459 (Flg. 3) at onestation is now lighted as well as supervisory lamp 477 (Fig. 4) at thesecond station. When the second .station disconnects, relay 449 (Fig. 3)at that point will release and, after an interval, relay 463 w1llrelease and light supervisory lamp 459, as previously described. Thiswill have no effeet on the toll line circuit, however, as re lay 464(Fig. 4) is held operated as prev1- ously described. When bothsubscribers have cleared out, both supervisory lamps will be lighted atone toll board and supervisory lamp 459 (Fig. 3) alone lighted at theother board. Both operators should then.'pull down their cords,restoring the circuits to normal.

ToZZ Zine to toll Zine coml For establishing through connections betweentwo central stations the toll line to toll line or through cord shown ascircuit K (Fig. 4) should be used. The operator will normally answersuch calls with the station to toll line cord I, previously described,and on finding that a.v through connection to a distant city is desiredascertains the statlon wanted and then substitutes a through cord Ttwill be understoodthat the twocord plugs 494 and 495 of this circuitare, whenthe cordis connected, plugged into jacks 387 (Fig. 5) of twoseparate toll line circuits J. In this cordcircuit, the tip of cordplug`494 (Fig. 4) is connected to the sleeve of the cord plug 495 andvice versa so that when two toll line circuits are interconnected, thesendln leg of each toll line is interconnected to t e receiving leg ofthe other toll line, sulicientresistance being included in the cordcircuit to lower the current in the pole changer 385 (Fig. 5) to theusual value of about 60 milliamperes. Under these conditions the twoduplex sets are connected together so as to form a' full duplex repeaterand incoming signals from either toll line will be repeated throughtothe other line. It is to be noted that this circuit operatesdifferently from station to toll line cord circuit J which as previouslypointed out operates over the same toll line as a half .duplex repeaterby reason of relay 464 which will repeat signals only in one direction.

The relays in the cord circuit K are not used for repeating signals fromone toll line to the other but serve to enable the local operator toconnecther printer into the circuit current when the cord is not in useand to extinguish the supervisory lamps. Relays 496 and 497 serve thispurpose. These relays each have two windings, one of low resistance 498and 49.9 and one of high resistance 500 and 501, and are capable ofoperating on a low current. The same type of relay as relay 101 (Fig. 2)in the customers stations circuit C may bepreferably used for thispurpose, but it is not necessary to use a polar relay if a sufficientlysensitive neutral relay is available. j

Assuming that plug 494 has been plugged into a toll line jack 387 (Fig.5) over which ya call has been received from a distant central station,current from source 414 associated with ground 415, will be passedthrough resistance 413, winding 398 of relay 385, conductor 410, contact411 of jack 387, to the sleeve of plug 494 (Fig. 4) and so overconductor 510 through winding 511 of relay 512 and through windings 498and 500 of polar relay 496 in series aiding, and so through re-vsistance 520 to ground 521. Relay 496 will be operated but since thehigh'resistance winding 500`of this .relay and resistance 520 in serieswith it, hold the current to about of relay 496 contact 538 is closedand ground 521 is resultingly` placed on a circuit traced as follows:from contact,538 to junction 801, conductor 550, winding 549 of relay522conl ductor 548, winding 547 of relay 523, conductor 546, winding545of relay 508, 'conductor 544, winding 543 of relay 512, conductor542,

resistance 541 and lthrough current source' 540 to ground 806. Thisplaces a biasing current of about 30 milliamperes on the four relaysjust mentioned. The closing of con- -tact 538 also closes a circuittraced from cur- 'operating them and closing the two cord circuits atcontacts 503 and 517, respectively..

It may be assumed that plug 495 will be plugged into an idle jack 387(Fig. 5) of an idle toll line connected to the distant called stationbefore slow operating relays 559 (Fig. 4) and 560 (since the operatorhas ascertained the name or number of the called station before pluggingup either plug or cord K) `can operate, in which case the'circuit fromthe tip of plug 494 to the sleeve of plug 495 will be closed and thecircuit from 3 milliamperes relays 385 (Fig. 5) and 512 (Fig. 4) willnot operate. AOn the operation

